Synthetic absorbable polyesters are well known in the art. The open and patent literature particularly describe absorbable polymers and copolymers made from glycolide, L(−)-lactide, D(+)-lactide, meso-lactide, epsilon-caprolactone, p-dioxanone, and trimethylene carbonate. The term absorbable is meant to be a generic term, which may also include bioabsorbable, resorbable, bioresorbable, degradable or biodegradable.
One very important application of absorbable polyesters is their use as surgical sutures. Absorbable sutures generally come in two basic forms, multifilament braids and monofilament fibers. For a polymer to function as a monofilament, it must generally possess a glass transition temperature, Tg, below room temperature. A low Tg helps to insure a low Young's modulus which in turn leads to filaments that are soft and pliable. A high Tg material would result in a wire-like fiber that would lead to relatively difficult handling sutures; in this art such sutures would be referred to or described as having a poor “hand”. If a polymer possesses a high Tg, and it is to be made into a suture, it invariably must be a construction based on multifilament yarns; a good example of this is a braid construction. It is known that monofilament sutures may have advantages versus multifilament sutures. Advantages of monofilament structures include a lower surface area, with less tissue drag during insertion into the tissue, with possibly less tissue reaction. Other advantages include no wicking into interstices between filaments in which bacteria can move and locate. There is some thought that infectious fluids might more easily move along the length of a multifilament construction through the interstices; this of course cannot happen in monofilaments. Monofilament fiber is generally easier to manufacture as there are none of the braiding steps usually associated with multifilament yarns.
Absorbable monofilaments sutures have been made from poly(p-dioxanone) and other low Tg polymers. A very important aspect of any absorbable medical device is the length of time that its mechanical properties are retained in vivo. For example, in some surgical applications it is important to retain strength for a considerable length of time to allow the body the time necessary to heal while performing its desired function. Slowly healing situations include, for example, diabetic patients or bodily areas having poor blood supply. Absorbable long term sutures have been made from conventional polymers, primarily made from lactide. Examples include a braided suture made from a high-lactide, and lactide/glycolide copolymer. In this art, those skilled in the art will appreciate that it is clear that monofilament and multifilament absorbable sutures exist and that short term and long term absorbable sutures exist. What does not presently exist is an absorbable polymer that can be made into a suture that is soft enough to be made into a monofilament and maintain its properties post-implantation to function long term. There then remains a problem of providing such a polymer, and there is a need not only for such a polymer, but also a need for a suture made from such a polymer. It is to be understood that these polymers would also be useful in the construction of fabrics such as surgical meshes.
Beside the opportunities in long term sutures and meshes, there exists opportunities for such polymers in devices that must be made from a deformable resin, ideally fabricated by known and conventional methods such as and including injection molding.
Crystalline block copolymers of epsilon-caprolactone and p-dioxanone are disclosed in U.S. Pat. No. 5,047,048 (Bezwada et al.). The copolymers covered in the patent range from about 5 to about 40 weight percent epsilon-caprolactone and the absorption profile is similar to poly(p-dioxanone). Furthermore, this reference describes the copolymers of p-dioxanone and epsilon-caprolactone made in random or block, segmented configuration of both, A-B and A-B-A types. Segmented copolymers of A-B-A type contain middle section “B” made from 100% epsilon-caprolactone, while end-blocks “A” are made of polymerized p-dioxanone only. Monofilaments made from these copolymers exhibit mechanical and hydrolysis properties similar to p-dioxanone homopolymer, with Young's modulus of elasticity only slightly lower than the p-dioxanone homopolymer (100 percent polymerized p-dioxanone). It is expected that fibers made from these epsilon-caprolactone/p-dioxanone copolymers, rich in p-dioxanone, would retain their mechanical properties post-implantation similar to p-dioxanone homopolymer. There then remains a strong need for a material that exhibits significantly lower Young's modulus of elasticity (i.e., better pliability) than that exhibited by the copolymers of the '048 patent to allow fabrication into soft monofilament fibers useful as suture or mesh components. In addition, there is a need for a monofilament that could retain mechanical properties, such as Breaking Strength Retention (BSR), longer than that exhibited by the copolymers of the '048 patent.
US 2013/0005829 A1 (Jamiolkowski et al.) discloses segmented epsilon-caprolactone-rich poly(epsi/on-caprolactone-co-p-dioxanone) copolymers of A-B-A type for use in long-term absorbable medical applications. The main disadvantage of these copolymers is their low melting point temperature (55-60° C.), which may make them thermally and physically unstable during various processing and storage conditions where higher temperatures are present (e.g., EO sterilization, exposure to hot temperatures during shipping, etc.). In addition, initial strength of the monofilaments made from these copolymers is relatively low, and their BSR properties are much longer than practically needed. Although these polymers are useful, there is still need for a monofilament suture that exhibits high thermal stability, high initial strength, and favorable BSR properties.
U.S. Pat. No. 5,314,989 (Kennedy et al.), entitled “Absorbable Composition”, describes a block copolymer for use in the fabrication of absorbable articles such as monofilament surgical sutures. The copolymer is prepared by copolymerizing one or more hard phase forming monomers and 1,4-dioxan-2-one, and then polymerizing one or more hard phase forming monomers with the dioxanone-containing copolymer. The materials of this invention require a hard phase, which is not within the scope of the present invention.
Similarly, U.S. Pat. No. 5,522,841 (Roby et al.), entitled “Absorbable Block Copolymers and Surgical Articles Fabricated Therefrom”, describes absorbable surgical articles formed from a block copolymer having one of the blocks made from hard phase forming monomers and another of the blocks made from random copolymers of soft phase forming monomers. Hard phase forming monomers are said to include glycolide and lactide while soft phase forming monomers include 1,4-dioxane-2-one and 1,3-dioxane-2-one and caprolactone.
U.S. Pat. No. 5,705,181 (Cooper et al.), entitled “Method of Making Absorbable Polymer Blends of Polylactides, Polycaprolactone and Polydioxanone”, describes absorbable binary and tertiary blends of homopolymers and copolymers of poly(lactide), poly(glycolide), poly(ε-caprolactone), and poly(p-dioxanone). These materials are blends and not copolymers.
There is a need in this art for novel, long term absorbable sutures that have good handling characteristics and strength retention. There is a further need in this art for novel absorbable polymer compositions for manufacturing such sutures and other absorbable medical devices.